1. Technical Field
The present invention relates to an optical disc apparatus which reads and writes data to an optical disc such as a CD, an MD, or a DVD.
Particularly, the invention relates to a control of a track jump in which a pickup head is moved to an objective track formed in a recording surface of an optical disc.
2. Related Art
Conventionally, there is an optical disc apparatus which reads data recorded on an optical disc such as a CD, an MD, or a DVD, and which writes data to such an optical disc. In an optical disc, a plurality of tracks are formed concentrically or spirally on a recording face. An optical disc apparatus detects a reflected light beam of a light beam illuminating the tracks to read out recorded data, and irradiates the tracks with a light beam to write data thereto.
When data recorded on an optical disc are to be read out, or when data are to be recorded to an optical disc, an optical disc apparatus performs a track jump for moving a pickup head to an objective one of many tracks formed in a recording surface of the optical disc. An objective track is a track from which data are to be read out, or into which data are to be written. A track jump is an operation of moving an illumination position of a light beam in a radial direction of the optical disc to place the illumination position of the light beam on the objective track.
Hereinafter, a track jump will be described. In a track jump, used is a tracking error signal indicative of the degree of deviation in a radial direction between the illumination position of the light beam and a track formed in the recording surface. The tracking error signal is obtained from a light beam which is reflected from the optical disc, and which is detected while moving the illumination position of the light beam in a radial direction of the optical disc.
In a usual optical disc apparatus, a pickup head is placed on a thread which is movable in a radial direction of an optical disc. A lens of the pickup head is attached so as to be movable on the thread in a radial direction of the optical disc. A track jump is conducted with moving the thread, or without moving the thread.
A track jump which is conducted with moving the thread will be described.
The optical disc apparatus moves the thread in a radial direction of the optical disc. This causes the main unit of the pickup head placed on the thread to be moved in a radial direction of the optical disc, and hence the center (the illumination position of the light beam) of the lens crosses sequentially tracks formed in the recording surface of the optical disc. At this time, also the movement of the lens of the pickup head with respect to the thread is conducted. A mirror portion which totally reflects a light beam is formed between adjacent tracks. A sinusoidal tracking error signal indicating that the center of the lens crosses a track is obtained from the amount of reflected light from the optical disc. One wavelength of the tracking error signal is produced each time the center of the lens crosses a track. When the wave number of the tracking error signal is counted, therefore, it is possible to obtain the number of tracks which the center of the lens has crossed.
Immediately before the start of a track jump, the optical disc apparatus calculates the number of tracks which are to be crossed before the center of the lens reaches the objective track position. Specifically, the number of tracks which are to be crossed is calculated from the difference between a track address indicative of the current track position of the pickup head, and that indicative of the objective track position. The current track position is obtained by reading data of the track.
When the center of the lens reaches a position which is separated by a certain distance from the objective track, the optical disc apparatus stops the thread. For example, the thread is stopped when the center of the lens reaches a track which is 100 tracks short of the objective track. When the optical disc apparatus moves the thread in this way, the main unit of the pickup head is moved to the vicinity of the objective track.
The movement of the lens with respect to the thread is continued even after the thread is stopped, so that the center of the lens is kept to be moved toward the objective track. When it is judged from the counted wave number of the tracking error signal that the center of the lens reaches the objective track, the optical disc apparatus conducts a tracking servo control to attain a track-on in the objective track.
A tracking servo control is a control of positioning the center of the lens on the center of a track.
In the case where the movement velocity of the lens is not substantially zero, the track pull-in is sometimes failed even when a tracking servo control is conducted, and hence a track-on in the objective track cannot be attained. Therefore, a control is conducted so that, when the center of the lens reaches a position which is separated by a certain distance from the objective track, the movement velocity is gradually reduced, and, when the center of the lens reaches the objective track position, the movement velocity is made substantially zero.
For example, a method is proposed in which, when the center of a lens reaches the objective track position, a braking operation is conducted so as to make the movement velocity of the lens substantially zero, and a tracking servo control is then conducted (the Unexamined Japanese Patent Application Publication No. Hei08-263849).
An optical disc apparatus is proposed in which the movement velocity of a thread is made constant during a track jump, whereby the control of the timing of conducting a braking operation is facilitated (the Unexamined Japanese Patent Application Publication No.Hei10-340459). The publication discloses a technique in which the rotational speed of a thread motor for moving a thread is made constant, thereby making the movement velocity of the thread constant.
3. Problems to Be Solved
However, the amount of braking which is applied when it is detected that the center of the lens reaches the objective track position is constant. When the movement velocity of the lens immediately before a braking operation is conducted is high, therefore, the lens fails to stop in the objective track position, and overshoots the position. When the movement velocity of the lens immediately before a braking operation is conducted is low, the braking is excessively applied, and the center of the lens is sometimes returned with respect to an optical disc. In this context, the return does not mean a movement of the lens in the opposite direction, but means a phenomenon in which the relative movement direction of the lens with respect to the optical disc is oriented in a returning direction (the direction along which the lens is separated from the objective track) because of eccentricity of the optical disc or the like.
Conventionally, immediately after a braking operation is completed, a tracking servo control is conducted so as to attain a track-on in the objective track. However, it is not certain whether, at the timing when a braking operation is completed, the center of the lens is positioned on a track or in a mirror portion formed between tracks. When a tracking servo control is conducted while the center of the lens is positioned in a mirror portion, the drive control cannot be correctly performed, and the lens is sometimes returned or suddenly accelerated, thereby causing track slipping.
In a conventional optical disc apparatus, therefore, it is often that a track-on in the objective track is not attained and a track jump is again conducted. As a result, the time period required for attaining a track-on in the objective track is prolonged, and the reliability of the apparatus main unit is not excellent.
It is an object of the invention to provide an optical disc apparatus in which, when a movement of a lens is to be stopped, a braking operation of a degree corresponding to the movement velocity of the lens is conducted to enable a track-on to be surely performed in an objective track.
It is another object of the invention to provide an optical disc apparatus in which, when the center of a lens is positioned in a mirror portion, a tracking servo control is prevented from being conducted, so that track slipping is suppressed, to enable a track-on to be surely performed in an objective track.
In order to solve the problems, the optical disc apparatus of the invention is configured in the following manner.
(1) The optical disc apparatus comprises:
a pickup head which illuminates a recording surface of an optical disc with a light beam that is focused by a lens, and which detects a reflected light beam from the surface to read data recorded on the optical disc;
a lens moving section which moves the lens to move an illumination position of the light beam in a radial direction of the optical disc;
a tracking error signal producing section which produces a tracking error signal indicating that the illumination position of the light beam crosses a track formed on the optical disc;
a brake signal outputting section which outputs a brake signal for causing the lens moving section to stop the lens which is being moved in a radial direction of the optical disc; and
an amount of braking controlling section which controls an amount of braking due to the brake signal that is output by the brake signal outputting section, in accordance with a period of the tracking error signal.
In the above configuration, the lens moving section moves the lens of the pickup head to move the illumination position of the light beam in a radial direction of the optical disc. The tracking error signal producing section produces the tracking error signal indicating that the illumination position of the light beam crosses a track formed on the optical disc. The tracking error signal is a sinusoidal signal. The period of the tracking error signal is proportional to the movement velocity of the lens. The amount of braking controlling section controls the amount of braking for stopping the lens of the pickup head in accordance with the period of the tracking error signal.
As a result, the brake signal outputting section outputs a brake signal of the amount of braking which corresponds to the movement velocity of the lens, thereby stopping the lens. For example, when the movement velocity of the lens is high, a brake signal of a large amount of braking is output, and, when the movement velocity of the lens is low, a brake signal of a small amount of braking is output, whereby the lens can be stopped. Therefore, the illumination position of the light beam can be surely stopped on the objective track, and a track-on can be surely performed in the objective track.
(2) The amount of braking controlling section controls the level of the brake signal.
(3) The amount of braking controlling section controls the time period when the brake signal is output.
(4) The amount of braking controlling section controls the level of the brake signal, and a time period when the brake signal is output.
In the above configuration, the amount of braking is controlled by controlling one or both of the degree of braking and the time period of application of braking.
(5) The optical disc apparatus further comprises a track position detecting section which detects a track position illuminated with the light beam, on the basis of the tracking error signal, and
the brake signal outputting section outputs the brake signal when the illumination position of the light beam detected by the track position detecting section is moved a predetermined distance short of the objective track.
In the configuration, the timing of conducting a braking operation can be easily controlled.
(6) The predetermined distance is a half track.
(7) The apparatus further comprises a tracking servo controlling section which, when the illumination position of the light beam is placed on the track after the output of the brake signal by the brake signal outputting section is completed, starts application of a tracking servo control.
In the configuration, when the illumination position of the light beam is placed on the track after the output of the brake signal is completed, application of a tracking servo control is started. Therefore, track slipping can be surely prevented from occurring, and hence a track-on in an objective track can be performed more surely.
(8) The tracking servo controlling section conducts a track-on when the level of the tracking error signal is lowered below a predetermined level.
(9) The tracking servo controlling section conducts a track-on when the level of the tracking error signal is within a predetermined range and is lowering.